The paper presents results of determination of emission factors for CO, NOx and SO2 from combustion of wooden and various sorts of agricultural biofuels in a commercially available small scale pellet boiler. The emission factors (EF) were determined at three different power loads of the boiler and are presented in mass, LHV and utilizable energy form. The results show significant influence of operating conditions as well as conditions of the boiler itself. Comparison of the results with various literature data shown significant impact of the experimental procedure on CO EFs and turned out that definition of the experimental conditions is essential for relevance of the presented data. EFs for NOx and SO2 were found to be particularly affected by nitrogen and sulphur content in the biomass respectively. (C) 2015 Elsevier Ltd. All rights reserved.